Hi all,
The rollout of the Thumbnail style update has been postponed whilst the engineers look at how best to enable an optional border, for the few instances that really need it. Once that has been decided and written/tested/deployed, I'll send an update to these threads, and post wider announcements at the global equivalents of [[Help talk:Image markup]] (Q4618557).
Much thanks to everyone that gave useful feedback, here and on the various talkpages. Have a good weekend.